A method of welding optical fibers is already described in published French patent application n.degree. 2 386 830 of Apr. 6, 1977. In the above-mentioned patent application, the covered portions of the fibers are held by two multiple clamps disposed on either side of a series of positioning grooves lying in the axis of the fibers, said multiple clamps being movable parallel to the axes of the fibers with said covered portions to preposition the fibers with respect to said grooves and to position the ends of said bared portions face to face.
Said multiple clamps preferably have three positions: open, slightly tightened (so as to allow the fibers to slide), and tightened hard (so as to block the fibers for welding). However, the use of multiple clamps to hold fibers has some disadvantages: difficulty in adjusting the fiber clamping force, lack of simultaneity in the clamping of the various fibers, wear of the multiple clamps, damage caused to the fibers when they are blocked, etc.
German patent application N.degree. 2 640 500 also provides for the ends of two optical fibers to be welded in line with each other while holding them in grooves of support blocks by means of a vacuum in a duct disposed inside the support and by using a welding device between the blocks of the support and below the ends of the fibers. Such a method does not allow accurate alignment of the fiber ends which extend over an appreciable length beyond the support blocks and allows the optical fibers to be welded together only one by one.
Preferred methods in accordance with the present invention allow several optical fibers to be welded end to end simultaneously and with great accuracy on the fiber axes. Such methods also provide even and simultaneous tightening of the fibers while they are being positioned and welded, to prevent damage to the fibers when they are clamped and to allow longer use of the welding device without appreciable wear.